Some digital cameras, like their film counterparts, include a zoom lens with multiple focus modes, each focus mode having a different focusing range. For example, a zoom lens may have a macro focus mode and a normal focus mode. A macro focus mode allows the lens to focus on objects at a shorter minimum distance for a given focal length than the normal focus mode. This mode is convenient for taking extreme close ups.
Depending on the lens design, the range of available focal lengths in each focus mode may be different. In particular, the maximum focal length may be smaller in one focus mode than in the other. For example, a zoom lens may be designed to provide focal lengths of 35 mm to 105 mm in normal focus mode and 35 mm to 75 mm in macro focus mode. A user may zoom out to 105 mm while framing a subject in normal focus mode, only to decide that macro focus mode is the better choice. Upon switching to macro focus mode, however, the digital camera necessarily drops to a smaller focal length within the available range (e.g., 75 mm) for macro focus mode, forcing the user to reframe the picture.
It is thus apparent that there is a need in the art for an improved method and apparatus for maintaining a consistent effective focal length in a digital camera.